Method of affixing coatings on incandescent-lamp filaments



April 12, 1927.

1-1. K. RICHARDSON METHOD OF AFFIXING COATINGS 0N INCANDESCENT LAMP FILAMENTS.

A Filed July 2a. 1921 HENRY K EmHARDsoN ATTORNEY Patched Apr. 12,1927.,

HENRY UEELAND RICHARDSON; OF EAST ORANGEfNEW JERSE'Y, ASSIGNOB TO WESTINGEOUSE LAMP COMPANY, A'CORPORATION 0F PENNSYLVANIA.

v HETHUD 92E'A COATINGS 0N'. INCANDESCENT-LAMP FILAMENTS.

Appueamn mea my 2s, 1921.1 serial no. 488,133.

This invention relates to processes of combining rare. earths, alkaline earths or oxides with metals and, more particularly, it relates to the application of such earths 5 to incandescent lamp filaments.

An object of the invention is the provision of a novel method for firmly afiixing a coating of a rare earth or an alkaline earth to electrical conductors, such as lamp filaments, electrodes, v etc.

Another object of the invention is to so` afiix a coating of anv earth to a lamp filament that it may not readily be removed.`

Other objects of the invention will be apparent :from a reading of. the following description.

Heretoore, in the incandescentlighting art, it has been found advantageous to combine rare and alkaline earths with certain olowers; such as lamp filaments, to increase 2Jtsheir efiiciency and to obtain certain lighting effects. In combinin the earths with the filaments, certain di culties have developed and especially where such -earths have Vbeen applied as coatings, as, under o eration, they have cracked and broken ofi.

he present invention has to do with' a new method for firmly afiixing earths, as coatin s, to lamp filaments. the accompanying drawings, illustrating an apparatus for carrying out my invention;

Fig. l is 'a diagrammatic illustration of an apparatus for practicing the method;

Fig. 2 is a diagrammatic illustration of a modified form of apparatus; and

Fig. 3 is a side elevation of a lamp ernployed in theA apparatus for coating fila- -ments which are later to be sealed in other lamps.

In the drawings, and particularly in Fig. l 1, is shown an incandescent lamp 1 comprising an evacuated envelope 2 having a filament- 3 mounted therein. The degree of vacuum in the envelope ranges from `l to 100 microns to eficiently practice the invention.

Although coatings may be afiixed when the vacuum varies above or below the range indicated, the results obtained under such conditions are imperfect. A small amount of a selected earth 4 is introduced into the envelope 2 before the filament 3 is sealedV therein. powdered form and it is found that, as the fineness thereof increases, the coating is more readily and uniformly afiixed. The earth may be an oxide of any one of the following metals: Calcium, cerium, barium, thorium, strontium, or yttrium; or a mixture of two or more of the earths mentioned. ,d

Any suitable apparatusv may be employed for impressino` a high potential betweenvthe filament 3 and an exterior electrode 5 of substantial area, such as a sheet of tin foil, and co-operatively positioned withrespect to the earth. The apparatus illustrated has proved satisfactory 1n practicing my inven- The earth is employed in its tion and may consist of a direct-current generator 6 connected, through a reversing switch 7 to the primary winding of an induction coil 8 which is provided with an interrupter 9. Electrical ,conductors 10 and 11, respectively, lead to the filament 3 and the tin-foil electrode 5. {[n the operation of this apparatus, the high potential derived from the generator and the induction coil is impressed across the electrodes. The voltage impressed upon the electrodes 3 and 5 may be varied within wide limits, satisfactory results having been obtained using from 12,000 to 40,000 volts. `In using a direct-current generator as the source of energy, very satisfactory results are Aobtained by making the tin foil the more positive electrode.

It will be understood, that in using an in'- duction coi-l to generate high potential, an interrupted direct current is delivered to the primarywinding and alternating potential is developed in the secondary winding thereof, however the potential developed, although alternating, is biased to some degree, because the induced potential is greater upon breaking the primaryl circuit than upon making the primary circuit. By specitying that the tin foil is made the more positive electrode, itis intended, as will be obvious, that the electrode 5 is positive uponfthe breaking of the primary circuit.

. In the early stage 'of impressing the high.

potential, it is noted'that, by reversing the direction ,ofthe current several times, the coating beglns to appear on the filament in pressing high potential across the electrodes,'

the filament becomes coated with the earth or oxide used. The action between the filament and the earth, in producing the desired result, cannot be completely accounted for in the present knowledge of the art. lt

it well known that a charged body attracts uncharged particles, and charged bodies attract each other when their charges are unlike in sign, but repel each other when their charges are alike. The operation, according to my invention, may therefore be explained rbecause the particles of earth or oxide are either not charged or charged to a potential different in sign from that of the filament 3 desired to be coated. That is, there is a potential difference between lilament 3 and the electrode 5, even though the applied current is alternating. I have demonstrated, after study and experiment, by thorough tests under operating conditions, that filaments coated as stated embody qualities which make them desirable, although it is not definitely known why the oxide sticks so firmly after being attracted to the filament.

The ease with which the earth is deposited may be increased by heating the filament as, for instance, by connecting the filament in series with a battery 12 which may be thrown into or out of the circuit by operating a switch 13.

1n Fig. 2 is illustrated a modified form of a lamp employed in successively performing additional experiments. This lamp is provided with a grid lit instead of a filament to be exhausted through the tube 19 in the usual manner, and the high potential is impressedas described above.

The method of affixing a coating to a metal or base has been described in connection with t-he coating ot' a filament but it is to be understood that it may be employed in ap lying earth to electrodes used in various e ectrical devices.

What is claimed is:

l. The method of afixing a coating of a metallic oxide to any 'elect-rode comprising aaaaori connecting the electrode, in a raried atmosphere in the presence of the metallic oxide in powdered iorm,`with an other electrode in an electric circuit, and impressing a high potential between said electrodes to cause a bodily transfer of the powdered particles to the electrode Without dissociation thereof.

2. The method or" afiixing a refractory .metallic compound onto a filament-ary inaterial .in a firmly adherent manner which consists in disposing the filamentary material adjacent said compound in a vacuum and creating an electrical difierence of potential of large magnitude between said lila-` mentary material and said compound to effect a bodily transfer of the compound to the filamentary material without dissociation thereof.

'3. The method of coating a filament with a firmly adherent deposit of an earth comprising mounting the filament in an envelope in an electrical circuit, impressing a high potential between said filament and the electrode and subsequently reversing thev direction of lthe applied oten'tial.-

5. The method of a 'ing an. earth to a filament comprising mounting the filament in an evacuated envelope having an electrode associated therewith, introducing such earth therein in powdered form, impressing a high potential between said filament and the elec trode to cause a bodily transfer of the powdered earth to thel filament and heating said filament by inde endent means.

6. The metho of manufacturing oxidecoated filamentary material comprising plac- -having a rarified atmosphere and containing ing-some alkaline earth in powdered forml in -1 a vessel adapted to be-evacuated, providing an external electrode for said vessel below the alkaline earth, inserting filametary ma'- 'terial into said vessel above the alkaline earth, evacuating said vessel and impressing a high potential between the electrode and `trede for said vessel below the oxide, in-

serting filamentary material into said vessel about the oxide, evacuating said vessel and impressing a high potential between the electrode and the filamentary material, while maintaining said material ina heated condition, from an tricity.

independent source of elecelectrie device comprising an evacu- 5 ated vessel provided with some earth in powdered form, electrode cooperating w means for impressing a a filament sealed therein, an

ith said earth and high potential besubscribed my name this 27th'day of July, 1921.

HENRY KNEELAND RICHARDSON. 

